1. Field of the Disclosure
The present invention relates to an inverter vector driving system and a method for estimating capacitance using the same, and more particularly, an inverter vector driving system for monitoring a degradation state of a capacitor of a DC-link in a power converting device including a PWM inverter and a method for estimating capacitance using the same.
2. Description of the Related Art
Generally, a fault of a DC-link capacitor accounts for a greater part of fault types of an alternating current (AC) motor drive system. The DC-link capacitor has characteristics of decreased capacitance and increased equivalent series resistance (ESR) due to its aging effect. When capacitance is reduced by more than 20% from the initial value, the capacitor is regarded as having reached the end of its lifespan. Therefore, a technique of estimating capacitance of the DC-link capacitor in a motor drive system is essential to maintain and manage a power converting device.
The most common method for identifying capacitance of the capacitor is to use an offline measurement technique. However, this method has a problem in that, because the capacitor is separated first from the power converting device and the capacitance should be then measured using an RLC meter, a system should stop operating for measurement and the capacitor should be separated from the system.
Unlike the offline measurement technique, an online estimation technique makes it possible to estimate capacitance while the motor is being operated. There are several exemplary online estimation techniques. Among them, a technique of estimating parameters of the capacitor in a variable speed drive system includes a method of estimating capacitance of the capacitor by measuring the DC component of the capacitor current and the average variation of the capacitor and DC-link voltages during the discharging mode of capacitors in which the motor is not operated.
In addition, a technique of estimating parameters of the capacitor during deceleration of the motor's speed in a brushless DC motor system has also been presented. In this case, since calculation of the capacitance is performed only once during an estimation process, reliability of the estimation decreases. In addition, a technique of estimating capacitance using ripple components of a current and a voltage of the capacitor while the motor is normally operated has been used in the aerospace industry, but this technique has a drawback in that the DC-link requires an additional current sensor.
Background technology of the present invention has been disclosed in Korean Patent Laid-Open Publication No. 2014-013730 (Laid-open on Feb. 5, 2014).